Sowing and Growing Sans Soil
You will raise most of the plants for your classroom hydroponic garden from seed, but you can start houseplants and many herbs for cuttings of mature plants. If you have a simple system without pumps or other forms of aeration, your best bets are the following:
- annual flowers such as marigolds, zinnias, nasturtiums
- bell peppers
- corn (in tubes)
Growing From Seed
You can start seeds in cotton, cubes of rockwool, peat plugs, perlite, or sand. After planting seeds, check regularly to make sure seeds remain moist, but are not water logged or moldy. If they are too wet, there may not be enough air for seeds to germinate properly. Some seeds, like beans and corn, will germinate in just a few days. Some others, such as tomato, bell pepper, and herbs may take as long as two weeks until they appear. If you do not see any sign of life after two weeks, it is best to replant the seeds.
After the true leaves form and a seedling is from one to several inches tall, you can transplant it into your system. Transplanting a seedling can be very stressful for a plant. Gently and carefully remove the plant, taking care not to damage the roots. A seedling, when transplanted into a bigger growing unit, is stressed at first. Some hydroponic gardeners recommend starting with half-strength nutrient solution, or initially spraying the leaves with nutrient solution rather than spraying or submerging roots, to minimize stress.
Houseplants such as coleus, tradescantia, heartleaf philodendron, pothos, and geranium grow quite well from cuttings. Rockwool cubes soaked in a 25 percent nutrient solution are nice for starting cuttings. You can also use moist perlite or sand. Cuttings root more quickly if they're covered with a plastic dome or misted regularly to maintain a humid environment.
A Few Plant Care Tips
As with plants grown in soil, your hydroponic unit seedlings and cuttings require ongoing care. Here are a few general suggestions:
- Plan space accordingly. Leafy and vining plants need room to spread out; provide support or trellising for such plants as tomatoes and cucumbers.
- Grow disease- and pest-resistant plant varieties. (Good growing practices should minimize disease and pest problems.)
- Practice good hygiene.(Without soil to filter contaminants, the liquid solution can transport impurities.) Wash hands before and after working with plants. Start with clean containers (a cleaning solution of 1 part bleach to 9 parts water is recommended).
- Observe plants carefully for signs of insect pests. Aphids, spider mites, and white flies go for lush growth. Either hand-pick pests, wash plants gently with a mild soap
- Change the nutrient solution regularly. Depending on the type of system you're using, you should change the nutrients every 1 to 3 weeks or so. Try to keep the pH between 5.8 and 6.5, the water temperature at around 70 degrees F, and the reservoir full.
- Plan ahead for vacations. If the setups are small enough, you might send hydroponic gardens home with students. If your unit is large and has an automatic aeration/circulation pump, it can be left running, but be sure to let someone know it is on. Make sure the nutrient solution container is filled before you leave, and that automatic lights are correctly working on a timer. Some schools plan hydroponics projects to coincide with semesters or terms, to avoid the problem altogether.